In a cement free knee joint replacement, additional stabilisation of a tibia platform by means of Spongiosa screws is the state of the art. In addition to the screws, often pegs, webs or ribs which are connected to the plateau, are common. The advantage of screws lies in the fact that, as a result of the initial stress produced thereby, a compression force is produced between the tibia platform and the bone during implantation. As a result, the primary stability is increased. Furthermore, bone is encouraged to grow into the distal or rear surface of the tibia platform. However, anchoring with screws has the disadvantage that the latter can be displaced backwards if osteonecroses or osteolyses occur under the tibia platform. Furthermore, the danger exists in the previously mentioned construction that detached polyethylene particles which originate from the polyethylene inlay mounted on the proximal side are displaced through the screw holes formed in the tibia platform into the bone. This then leads to local osteolyses.
In the relevant literature, there are described various cylindrical expansion anchors on the distal side of the tibia platform. These have the advantage that they make a pretension force possible. However, since they are based on the expansion principle there is no assurance that the anchor remains securely connected to the tibia platform. The possibility exists of being displaced and hence the formation of a gap between expansion anchor and tibia plateau. Polyethylene particles, coming from the mentioned inlay, may be displaced through this gap into the bone and lead to osteolyses. In addition, the point shaped support which is produced by anchors is disadvantageous for a long term osteointegration of the implant.
As an alternative to short anchors, a long intramedullar support can be used. This support can be completed by ribs by means of which a somewhat more widespread supporting of the tibia platform is obtained. A construction of this type is known e.g. from U.S. Pat. No. 4,938,769. The use of an intramedullar support has the disadvantage however that the load transference takes place in the distal region. The proximal bone beneath the tibia platform is in contrast only slightly stressed. This effect, so called "stress shielding" leads to bone resorption and in the long term to loosening of the implant.